Linear公司的LT396是具有I2C接口的雙路同步降壓DC疍C轉換器,工作在恒流和恒壓源模式,非常適合于LED驅動器.工作電壓4V－36V,恒流穩流±3%,1000:1外接真彩色PWM調光,10:1外接模擬調光,可調開關頻率200kHz-2MHz,主要用在通用,工業,醫療和汽車照明,恒流和恒壓源.本文介紹了LT3964主要特性,框圖和多種應用電路,以及演示板DC2424A主要特性,電路圖和材料清單.

The LTR3964 is a dual synchronous step-down DC／DCconverter with I2C interface designed to operate as aconstant-current and constant-voltage source and is idealfor driving LEDs. The fixed frequency and peak currentmode topology result in stable operation over a wide rangeof supply and output voltages. The ground referred voltage FB pin serves as the input for several LED protectionfeatures, and also allows the converter to operate as aconstant-voltage source. The maximum output current isset by an external resistor, and the output current amplifierhas a rail-to-rail common mode range. LT3964 usesan I2C interface to communicate with a microcontrollerto read LED faults, write PWM and analog dimming registersand set fault masking. The I2C PWM input providesLED dimming ratios up to 8192:1. The I2C programmableCTRL register sets the gain of the external CTRL pin, andmaximum current sense threshold, providing additional analog dimming capability.

LT3964主要特性:

Wide Input Voltage Range: 4V to 36V
Two Independent 1.6A／40V Synchronous Bucks
I2C Interface for Internal True Color PWM? Dimming(8192:1), Analog Dimming and Fault Reporting
1000:1 External True Color PWM Dimming and10:1 External Analog Dimming
PMOS Switch Driver for PWM and Output Disconnect
±3% Constant Current Regulation
Adjustable Frequency: 200kHz to 2MHz
Frequency Synchronization with Clock Output
Programmable OPENLED Protection with Reporting
Short-Circuit Protection with Reporting
Programmable Undervoltage Lockout with Hysteresis
Internal Compensation
9 Unique Device Addresses for I2C
Available in 5mm × 6mm 36-Lead QFN Package

LT3964應用:

General Purpose, Industrial, Medical andAutomotive Lighting
Constant-Current, Constant-Voltage Source
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圖1.LT3964框圖

圖2.LT3964應用電路(1):50W雙路降壓1A LED驅動器

圖3.LT3964應用電路(2):帶PWM調光50W雙路降壓1A LED驅動

圖4.LT3964應用電路(3):多路升壓／降壓倒LED驅動器

圖5.LT3964應用電路(4):矩陣LED驅動器

演示板DC2424A

The DC2424A is a 36V synchronous dual LED driver withI2C featuring the LT?3964. It drives two separate LEDs(or channels of LEDs) at 1A when VIN is between 5Vand 36V. DC2424A runs at 2MHz switching frequency.

Its two channels can drive separate LED strings whichcan have different currents, voltages, or dimming ratios.It can be controlled with I2C communications or it canbe run in non-I2C mode with proper ADDR pin settings.

It is protected against both open and short LED conditionsand reports the faults. In I2C mode, faults can beenabled or disabled. Up to 9 different DC2424As can beplaced on the same I2C bus with unique addresses. Agraphical user interface (GUI) is available through QuikEval? when connected to a DC2026C Linduino? Onedemo circuit.

The LT3964 has an input voltage range from 4V to 36V. Ithas two independent 1.6A, 40V bucks with internal, synchronous40V switches for high efficiency and small size.

It has adjustable switching frequency between 200kHzand 2MHz. It can be synchronized to an external sourceor programmed with a clock output (CLKOUT) from theserial interface. The PWMTG high side PWM MOSFETdrivers assist with short-circuit protection and versatility.

Although the demo circuit is optimized for just one LEDper channel, it can be altered to be buck regulators withas high as 33V of LEDs if VIN is high enough and circuitcomponents are changed appropriately.

In non-I2C mode, each channel can separately be PWMandanalog-dimmed by placing a PWM signal or CTRLvoltage on the provided turrets. In I2C mode, each channelcan be dimmed to up to 8192:1 and analog dimmed to ahigh ratio using serial communications. Small ceramic input and output capacitors are used tosave space and cost. The open LED overvoltage protectionuses the IC’s constant voltage regulation loop to regulatethe output to approximately 4.2V if the LED stringis opened. There is a protection diode from each LED+to GND to prevent negative ringing during a short-circuitcondition.

Undervoltage lockout can be adjusted on the circuit with afew simple resistor choices. The output voltage (overvoltageprotection) can be adjusted by changing the feedback resistors for higher string voltages. Other componentsmay need to be changed to accommodate higher voltagesalso.

The LT3964 data sheet gives a complete description ofthe device, operation and applications information. Thedata sheet must be read in conjunction with this demomanual for DC2424A. The LT3964EUHE is assembled in a36-lead plastic 5mmx6mm QFN package with a thermallyenhanced ground pad. Proper board layout is essentialfor maximum thermal performance. See the data sheetLayout Considerations section.
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圖6.演示板DC2424A測試建立圖

圖7.演示板DC2424A電路圖
演示板DC2424A材料清單: